Quaternary Strata in CRP-1, Cape Roberts Project, Antarctica

The uppermost part of the core in Cape Roberts Project -1 (CRP-1), to 43.55 mbsf, is interpreted to be Quaternary in age. The interval comprises poorly consolidated clays, silts, sands, gravels, diamictons, and an association of mixed skeletal carbonate-terrigenous clastic sediments. The interval has been divided into four principal lithostratigraphic units based on major changes in lithology. Some of these units have been further subdivided. Notable within the Quaternary interval is a short section (c. 32-34 mbsf) of mixed skeletal carbonate -terrigenous clastic sediment which contains a rich and diverse assemblage of benthic macroinvertebrate fossils. Petrological investigations of large clasts and sands suggests that Quaternary sediments in CRP-1 were derived from a variety of basement sources including Precambrian to Early Palaeozoic metamorphic and granitic rocks, Jurassic dolerites, and the Devonian - Triassic Beacon Supergroup, with a variable though significant contribution from coeval volcanic activity associated with the McMurdo Volcanic Group. The Quaternary section of CRP-1 is dated by diatom biostratigraphy at 1.25 - 1.8 Ma, and has also yielded a wide variety of macrofossils and microfossils. Diatoms are the most prevalent fossil group, foraminifers are also ubiquitous, palynomorphs more restricted in occurrence and nannofossils scarce. The assemblage contains the first report of the calcareous dinoflagellate Thoracosphaera from the Quaternary of the East Antarctic margin. The invertebrate assemblage, which is virtually in situ, is dominated by molluscs, with appreciable numbers of bryozoans and lesser numbers of echinoids, serpulid worms, octocorals, barnacles and brachiopods. The section is interpreted to represent shallow-marine depositional environments that experienced considerable variations in climate and proximity to ice, ranging from 1) possible terrestrial exposure during sea-level lowstand, 2) glaciomarine deposition under the influence of nearby glacial ice, 3) deposition under seasonal sea-ice, similar to today, to 4) times of warmer-marine temperatures when carbonate sediments accumulated beneath seas that lacked sea-ice. At least two cycles of relative sea-level rise and fall are recognised from a sequence stratigraphic analysis.